STRUCTURAL TIMBER DESIGN PER BS 5268, 2:2002
This post is written aiming at giving tips and summary of understanding modification factors on a timber design designing for various.
There are various things to be condsidered when considering modification factors for structural timber design. There are generally usage conditions for a particular timber. The following are the modifiction factors for structural timber design under BS 5268,2:2002.
K2 - Modification factor for weather conditions. This is the modification factor which can modify dry stress to wet stress, this is used when a timber is well seasoned and it is going to bes used in wet conditions. It will not be applied when a timber is in wet condition and is going to be used for in wet coditions.
Not only that one but also it is going to be used when a timber is dry and is going to be use in dry condiitions, The values of K2 can be found on table 16 of BS 5268 on page 32 (7). On that table you can see that as a timber exposed to bending, tension, compression and shear stresses, there is a way strength can be reduced as in table 16.
K3 - Modification factor for loading duration. When a timber is used for long period of time its capacity of carrying load tend to be reduced, also when a timber is used for a short period of time its carrying capacity of carrying load it is greater. For example when you have a car made of timber materials it can carry a huge load in a short period of time but not for a long time use.
Consider a table 17 of BS 5268,2:2002 on page number 32 (7).
K4 - Modification factor for bearing stress, consider a table 18 on page 34 (9).
Notre if your value is not found on that table interpolation is allowed so as to ger your entire values
K5 - Modification factor for shear on notched end timbers. Consider a page 34 of BS, for a timber notched on the top and a timber notched on the underside (9).
K6 - Form factor. Things to be considered over here is that it is not applicable for timber mebers with rectengular cross sections. For other cross section shapes K6 can be used as follows,
k = 1.18 for a solid circular sections, and
k = 1.41 for solid square sections loaded diagonal.
K7 - Modificatioon factor for depth. This modification is used only size of timber is not 300mm, since values in table 8 are only prepared for timber with depth h, of 300mm. For other depths should then be modified by values given in page 36 of BS (11)
